1. Field of the Disclosure
This disclosure relates in general to transparent conductors having workfunction greater than 4.7 eV for use in electronic devices.
2. Description of the Related Art
Organic electronic devices define a category of products that include an active layer. Such devices convert electrical energy into radiation, detect signals through electronic processes, convert radiation into electrical energy, or include one or more organic semiconductor layers.
Organic light-emitting diodes (OLEDs) are organic electronic devices comprising an organic layer capable of electroluminescence. OLEDs containing conducting polymers can have the following configuration which may include additional optional layers, materials or compositions:                anode/buffer layer/EL material/cathodeThe anode is typically any material that has the ability to inject holes into the electroluminescent (“EL”) material, such as, for example, indium/tin oxide (ITO). The anode is optionally supported on a glass or plastic substrate. The buffer layer is typically an electrically conducting polymer and facilitates the injection of holes from the anode into the EL material layer. EL materials include fluorescent compounds, fluorescent and phosphorescent metal complexes, conjugated polymers, and combinations and mixtures thereof. The cathode is typically any material (such as, e.g., Ca or Ba) that has the ability to inject electrons into the EL material. At least one of the anode or cathode is transparent or semi-transparent to allow for light emission.        
ITO is frequently used as the transparent anode. However, the work function of ITO is relatively low, typically in the range of 4.6 eV. This low work function results in less effective injection of holes into the EL material. In some cases, the work function of ITO can be improved (i.e., raised) by surface treatment. However, these treatments are sometime not stable and result in reduced device lifetime.
It is known that conductive carbon nanotube (“CNT”) dispersions can be used to form transparent, conductive films. The films have conductivity of about 6×103 S/cm (Science, p1273-1276, vol 305, Aug. 27, 2004), which is similar to the conductivity of indium/tin oxide vapor-deposited on substrates. It is evident that CNT film could replace ITO as a transparent anode. However, the work function of CNT is in the same range as that of ITO and is not high enough to inject holes to the light emitting layer for OLEDs applications.
Thus, there is a continuing need for improved materials to form transparent anodes.